This invention relates generally to landing gear for supporting a vehicle, and more particularly to landing gear for supporting a semitrailer adjacent its forward end when the trailer is uncoupled from a tractor used to pull the trailer.
Landing gear of the present invention is especially, but not exclusively, suited for semitrailers equipped with air suspensions, such as the air suspension shown in co-assigned U.S. Pat. No. 5,470,096. Suspensions of this type have air bladders connected between the trailer frame and the trailer axle to support the frame and isolate the trailer contents from shocks caused by rough roadway. These bladders are filled with air from a compressed air supply, such as a compressor on board the tractor used to pull the trailer. The bladders are filled with more air when the trailer is loaded than when it is empty to compensate for the increased weight of the load. If the trailer load is increased when the air supply is shut off, such as may occur when the trailer is loaded at a loading dock, the trailer tends to "walk" or move forward or rearward due to certain design features of the suspension. Similarly, a trailer sitting in a parked position for an extended period of time tends to move as air bleeds from the suspension. When the trailer moves and its forward end is supported by landing gear, bending loads are applied to the landing gear. These loads can damage the landing gear, particularly the threads on an internal screw shaft used to raise and lower the landing gear. Damage to these threads tends to make raising and lowering the landing gear more difficult. Although trailer "walk" can be avoided by venting air from the suspension so suspension movement is reduced, drivers often fail to take this precaution before parking the trailer or before loading or unloading it.
Reference may be made to U.S. Pat. Nos. 4,903,977 and 5,423,518 for examples of prior art relating to landing gear of the general type of this invention.